Guided wave propagation and skew effects in anisotropic carbon fiber reinforced laminates

Guided ultrasonic waves provide a promising structural health monitoring (SHM) solution for composite structures as they are able to propagate relatively long distances with low attenuation. However, the material anisotropy results in directionally dependent phase and group velocities, in addition to energy focusing, wave skewing, and beam spreading phenomena. These effects could lead to inaccurate damage localization if not accounted for. In this contribution, the guided wave propagation behavior (A0 mode) for a highly anisotropic, unidirectional carbon fiber reinforced polymer laminate is systematically investigated through both finite element analysis and non-contact laser measurements and compared to theoretical predictions. The directional dependency of phase and group velocity measured for a point and line source shows good agreement with theoretical predictions, once a correction for wave skew effects is applied. Wave skew angles were evaluated from the experimental and numerical wave propagation in multiple directions and matched theoretical predictions based on the phase slowness curve. Significant guided wave beam spreading from a line source was observed and quantified from both experiments and simulations and compared with theoretical predictions using the anisotropy factor. The impact of anisotropic guided wave propagation behavior on SHM is discussed

Anisotropy influence on guided wave scattering for composite structure monitoring

Composite structures are widely used for aerospace applications but are prone to barely visible impact damage from low velocity impacts. Guided wave measurements using sparse arrays of distributed sensors provide an important structural health monitoring (SHM) tool for detecting and localizing impact damage in composites. However, the anisotropy of composites needs to be considered as it can affect guided wave propagation and scattering, impacting imaging performance. Improved defect characterization can be achieved by considering the scattering characteristics for the signal processing. Scattering around two different damage types for multiple incident wave directions in a quasi-isotropic carbon fiber reinforced polymer (CFRP) panel were investigated. Full 3D Finite Element (FE) simulations were compared to the measured scattered guided wave field at an artificial insert delamination. Permanent magnets mounted on an undamaged region of the plate were used as scattering targets and both numerical and experimental scattering patterns were compared to the delamination results. Strong directional dependency was observed for both damage types, with energy focusing along the fiber directions of the outer ply layers. For the delamination, mostly forward scattering is observed for all incident wave directions, whereas the magnet blocked forward wave transmission and scattered wave energy in all directions. 2D scattering matrices were calculated, demonstrating distinct scattering behavior for each damage type. Implications of anisotropy and angular scattering on SHM guided wave sparse array imaging are discussed

High-frequency guided ultrasonic waves for hidden defect detection in multi-layered aircraft structures

AbstractAerospace structures often contain multi-layered metallic components where hidden defects such as fatigue cracks and localized disbonds can develop, necessitating non-destructive testing. Employing standard wedge transducers, high frequency guided ultrasonic waves that penetrate through the complete thickness were generated in a model structure consisting of two adhesively bonded aluminium plates. Interference occurs between the wave modes during propagation along the structure, resulting in a frequency dependent variation of the energy through the thickness with distance. The wave propagation along the specimen was measured experimentally using a laser interferometer. Good agreement with theoretical predictions and two-dimensional finite element simulations was found. Significant propagation distance with a strong, non-dispersive main wave pulse was achieved. The interaction of the high frequency guided ultrasonic waves with small notches in the aluminium layer facing the sealant and on the bottom surface of the multilayer structure was investigated. Standard pulse-echo measurements were conducted to verify the detection sensitivity and the influence of the stand-off distance predicted from the finite element simulations. The results demonstrated the potential of high frequency guided waves for hidden defect detection at critical and difficult to access locations in aerospace structures from a stand-off distance

Smart and secure medical device gateway for managing patient recovery

Patients recuperating from orthopedic surgery require frequent monitoring and hospital visits with a wealth of personal medical data generated both on and off-site, making it challenging to maintain records. This paper discusses a secure blockchain-based data management software to enable safe remote access without compromising patient information. The BlockTrack software developed at our group will be customized to interface with modules for orthopedic recuperation monitoring. Modules can consist of ultrasonic bone health monitoring sensors, connected to relay nodes that can transmit patient data to the BlockTrack mobile app, which then intercepts the information to be stored securely on a cloud-based Blockchain network. Each record will have a unique ID enabled by Blockchain, for secure access and review of patient information by other parties, including doctors and pharmacists. Key findings are discussed with a goal to further develop this solution

Guided ultrasonic wave monitoring techniques to assess bone implant loosening

Total ankle replacement (TAR) is the main clinical treatment for end-stage ankle arthritis, replacing the ankle joint with a metallic implant. Component loosening, fracture, and wear are the main reasons for implant failure, requiring revision surgery. A non-invasive guided wave monitoring technique is being developed to ultimately evaluate in-vivo implant device integrity and bone-implant interface conditions (osseointegration). Finite Element (FE) simulations were performed to investigate the feasibility and sensitivity of ultrasonic monitoring of the interface conditions, assessing suitable guide d wave modes and excitation frequencies. A simplified implant geometry was developed for FE modelling in Abaqus/Explicit. Selected guided wave modes (higher-order longitudinal modes sensitive to bone/implant interface changes) were excited at the distal end of the metallic implant component for detection of variations of bone-implant contact conditions. Simulation results showed the feasibility for guided ultrasonic waves to monitor bone implant osseointegration. Guided wave signal amplitude and changes of arrival time of pulses propagating along the metallic implant can indicate the presence of improved osseointegration. The potential for the integration of the bone implant monitoring sensors and other biosensors into secure, blockchain-based, remote patient data management systems will be further investigated

The effect of strontium and silicon substituted hydroxyapatite electrochemical coatings on bone ingrowth and osseointegration of selective laser sintered porous metal implants

Additive manufactured, porous bone implants have the potential to improve osseointegration and reduce failure rates of orthopaedic devices. Substantially porous implants are increasingly used in a number of orthopaedic applications. HA plasma spraying-a line of sight process-cannot coat the inner surfaces of substantially porous structures, whereas electrochemical deposition of calcium phosphate can fully coat the inner surfaces of porous implants for improved bioactivity, but the osseous response of different types of hydroxyapatite (HA) coatings with ionic substitutions has not been evaluated for implants in the same in vivo model. In this study, laser sintered Ti6Al4V implants with pore sizes of Ø 700 μm and Ø 1500 μm were electrochemically coated with HA, silicon-substituted HA (SiHA), and strontium-substituted HA (SrHA), and implanted in ovine femoral condylar defects. Implants were retrieved after 6 weeks and histological and histomorphometric evaluation were compared to electrochemically coated implants with uncoated and HA plasma sprayed controls. The HA, SiHA and SrHA coatings had Ca:P, Ca:(P+Si) and (Ca+Sr):P ratios of 1.53, 1.14 and 1.32 respectively. Electrochemically coated implants significantly promoted bone attachment to the implant surfaces of the inner pores and displayed improved osseointegration compared to uncoated scaffolds for both pore sizes (p<0.001), whereas bone ingrowth was restricted to the surface for HA plasma coated or uncoated implants. Electrochemically coated HA implants achieved the highest osseointegration, followed by SrHA coated implants, and both coatings exhibited significantly more bone growth than plasma sprayed groups (p≤0.01 for all 4 cases). SiHA had significantly more osseointegration when compared against the uncoated control, but no significant difference compared with other coatings. There was no significant difference in ingrowth or osseointegration between pore sizes, and the bone-implant-contact was significantly higher in the electrochemical HA than in SiHA or SrHA. These results suggest that osseointegration is insensitive to pore size, whereas surface modification through the presence of an osteoconductive coating plays an important role in improving osseointegration, which may be critically important for extensively porous implants

The effect of bone growth onto massive prostheses collars in protecting the implant from fracture

Limb-sparing distal femoral endoprotheses used in cancer patients have a high risk of aseptic loosening. It had been reported that young adolescent patients have a higher rate of loosening and fatigue fracture of intramedullary stems because the implant becomes undersized as patients grow. Extracortical bone growth into the grooved hydroxyapatite-coated collar had been shown to reduce failure rates. The stresses in the implant and femur have been calculated from Finite Element models for different stages of bone growth onto the collar. For a small diameter stem without any bone growth, a large stress concentration at the implant shoulder was found, leading to a significant fracture risk under normal walking loads. Bone growth and osseointergration onto the implant collar reduced the stress level in the implant to safe levels. For small bone bridges a risk of bone fracture was observed

A novel adaptive algorithm for 3D finite element analysis to model extracortical bone growth

Extracortical bone growth with osseointegration of bone onto the shaft of massive bone tumour implants is an important clinical outcome for long-term implant survival. A new computational algorithm combining geometrical shape changes and bone adaptation in 3D Finite Element simulations has been developed, using a soft tissue envelope mesh, a novel concept of osteoconnectivity, and bone remodelling theory. The effects of varying the initial tissue density, spatial influence function and time step were investigated. The methodology demonstrated good correspondence to radiological results for a segmental prosthesis

Novel adaptive finite element algorithms to predict bone ingrowth in additive manufactured porous implants

Bone loss caused by stress shielding of metallic implants is a concern, as it can potentially lead to long-term implant failure. Surface coating and reducing structural stiffness of implants are two ways to improve bone ingrowth and osteointegration. Additive manufacturing, through selective laser sintering (SLS) or electron beam melting (EBM) of metallic alloys, can produce porous implants with bone ingrowth regions that enhance osteointegration and improve clinical outcomes. Histology of porous Ti6Al4V plugs of two pore sizes with and without electrochemically deposited hydroxyapatite coating, implanted in ovine condyles, showed that bone formation did not penetrate deep into the porous structure, whilst significantly increased bone growth along coated pore surfaces (osteointegration) was observed. Finite Element simulations, combining new algorithms to model bone ingrowth and the effect of surface modification on osteoconduction, were verified with the histology results. The results showed stress shielding of porous implants made from conventional titanium alloy due to material stiffness and implant geometry, limiting ingrowth and osteointegration. Simulations for reduced implant material stiffness predicted increased bone ingrowth. For low modulus Titanium-tantalum alloy (Ti-70%Ta), reduced stress shielding and enhanced bone ingrowth into the porous implant was found, leading to improved mechanical interlock. Algorithms predicted osteoconductive coating to promote both osteointegration and bone ingrowth into the inner pores when they were coated. These new Finite Element algorithms show that using implant materials with lower elastic modulus, osteoconductive coatings or improved implant design could lead to increased bone remodelling that optimises tissue regeneration, fulfilling the potential of enhanced porosity and complex implant designs made possible by additive layer manufacturing techniques

Reduction in BACE1 decreases body weight, protects against diet-induced obesity and enhances insulin sensitivity in mice

Insulin resistance and impaired glucose homoeostasis are important indicators of Type 2 diabetes and are early risk factors of AD (Alzheimer's disease). An essential feature of AD pathology is the presence of BACE1 (β-site amyloid precursor protein-cleaving enzyme 1), which regulates production of toxic amyloid peptides. However, whether BACE1 also plays a role in glucose homoeostasis is presently unknown. We have used transgenic mice to analyse the effects of loss of BACE1 on body weight, and lipid and glucose homoeostasis. BACE1−/− mice are lean, with decreased adiposity, higher energy expenditure, and improved glucose disposal and peripheral insulin sensitivity than wild-type littermates. BACE1−/− mice are also protected from diet-induced obesity. BACE1-deficient skeletal muscle and liver exhibit improved insulin sensitivity. In a skeletal muscle cell line, BACE1 inhibition increased glucose uptake and enhanced insulin sensitivity. The loss of BACE1 is associated with increased levels of UCP1 (uncoupling protein 1) in BAT (brown adipose tissue) and UCP2 and UCP3 mRNA in skeletal muscle, indicative of increased uncoupled respiration and metabolic inefficiency. Thus BACE1 levels may play a critical role in glucose and lipid homoeostasis in conditions of chronic nutrient excess. Therefore strategies that ameliorate BACE1 activity may be important novel approaches for the treatment of diabetes